In order to produce electricity from a wind turbine, rotation of the wind turbines is transferred to an alternator, typically directly or through a transmission gear system. The alternator outputs an electromagnetic force (hereinafter “EMF”) that is proportional to the revolutions per minute (hereinafter “RPM”) of the alternator and to the strength of a magnetic field generated by relative movement of magnets to electromagnetic assemblies including coils wound around magnetic cores.
The need to capture more wind power, i.e., improve the conversion of the rotation of the wind turbine into electrical energy, is leading to an increase in the span of the turbine blades of the wind turbine. This, in turn, leads to lower RPM of the wind turbine. Consequently, a conventional wind turbine includes a transmission gear section that increases the RPM of the alternator. Some of the main disadvantages of this type of transmission gear section include: energy losses, lower overall efficiency, and higher weight and maintenance.
A wind turbine without a transmission gear section is often referred to as a direct drive wind turbine. A direct drive wind turbine alternator has a larger diameter, and there are two primary types of such alternators, a radial flux type and an axial flux type.
The present invention relates to axial flux alternators that usually include magnets and electromagnetic assemblies that move relative to one another and have an air gap therebetween. Constructing the alternator to provide a desired dimension for the air gap between the magnets and the coils of an axial flux alternator, also referred to herein as adjusting the air gap, and maintaining the air gap during operation of the wind turbine, is a technical challenge, particularly for a large diameter axial flux alternator.